Project 2: Glial development during glomerulus formation. Glia are understood to play important roles in development of the nervous system, but our understanding of the underlying mechanisms or indeed of the full repertoire of their involvement is rudimentary. In the olfactory system, in particular, experiments in a variety of systems suggest that glia contribute to the formation of the primary olfactory pathway, but direct tests of their role have been difficult. In Manduca, however, we have been able to experimentally generate glia-deficient animals and show that glia are essential for the formation of glomerular compartments in the antennal lobe (Oland and Tolbert, 19878, 1996; Oland et al., 1988, 1999), the most equivalent of the olfactory bulb. We have recently have discovered in the developing olfactory nerve an intriguing glia-rich region that induces a series of changes in olfactory receptor axons, including defasciculation, changes in trajectory, and refasciculation, as they entered the antennal lobe (Olfand et al., 1998; Appendix). In glia- deficient animals, the olfactory receptor axons leaving this sorting zone fail to fasciculate properly and many subsequently bypass their normal targets within the lobe (Rossler et al., 199), strongly implicating the glia in this region as critical players in axon sorting. With this proposal we intend to continue our focus on the role of glial cells in the formation of the primary olfactory of Manduca, now broadening our studiers to probe the glia-rich domain in the nerve. We will examine the development of the glial architecture of the sorting zone and determine precisely which axonal behaviors are affected by focal deletion of the sorting zone glia (Aim 1). We also will begin to explore the molecular basis for particular interactions between glial cells a and neurons that previous studies indicated underlie olfactory receptor axon sorting and glomerulus formation. Examination of interactions between glia and receptor axons and dendrites of antennal-lobe neurons both in co-culture and in organotypic cultures will indicates the classes of neuronal responses to the glia and provide the foundation for examining the function of tenascin-like molecules that previous experiments have indicated alter the growth of Manduca neurons (Aim 2). Given the remarkable organizational similarity of primary olfactory systems across phylogenetic boundaries, we expect our findings to provide broadly applicable insights into the glial role in development of olfactory pathways.